<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div id="box">
    <div id="test">
      <div id="son">123</div>
    </div>
  </div>

  <!-- 捕获 ： 从外面往里去找 -->
  <!-- 冒泡： 从里往外冒 -->

</body>
</html>